The present invention relates generally to X-ray imaging machines, and particularly to X-ray imaging machines that include dihedral cathode cups with cathode tabs for producing desired focal spot length profile.
A traditional X-ray imaging system employs an X-ray source and a detector array for producing an internal image of an object. The X-ray source generates X-rays which pass through the object. This object absorbs a portion of the X-rays as the X-rays are transmitted therethrough. As a result, the transmitted X-rays vary in intensity. The detector array receives and measures the resultant X-ray flux so as to generate the electrical signals necessary for constructing an internal image of the object.
Computed tomography (CT) imaging systems typically include a gantry that rotates at various speeds in order to create a 360xc2x0 image. The gantry contains a CT tube assembly that generates X-rays across a vacuum gap between a cathode and an anode. In order to generate the X-rays, a large voltage potential of approximately 120-140 kV is created across the vacuum gap allowing electrons, in the form of an electron beam, to be emitted from the cathode to be incident on the target of the anode. In releasing the electrons, a filament contained within the cathode is heated to incandescence by passing an electric current therein. The electrons are accelerated by the electric field and impinge on the target at a focal spot, whereby they are abruptly slowed down and directed at an impingement angle xcex1 of approximately 90xc2x0 so as to emit X-rays through a CT tube window.
The filament or electron source typically is a coiled tungsten wire that is heated to temperatures approaching 2600xc2x0 C. The electrons are accelerated by an electric field imposed between the cathode and the anode. The anode, in a high power X-ray tube designed for current CT devices, is a target having a target face that rotates at angular velocities of approximately 120 Hz or greater. This target may be comprised of molybdenum, graphite, and various other materials.
Cathode tabs typically are positioned adjacent to the filament in order to focus the X-ray flux or electron beam and produce a uniform focal spot length profile. Ordinarily, two cathode tabs are located on opposite ends of the filament. Existing tabs are L-shaped brackets that surround the filament. One portion of the bracket typically is fastened to the cathode cup while the other portion is utilized for directing the electron beam.
A drawback of existing cathode tabs is that meticulous alignment of these tabs on the cathode cup is usually necessary for producing the desired focal spot length profile. Ordinarily, CT scanner manufacturers carefully fasten each tab to the cathode cup in a specific predetermined position. This position is usually based on precise distances from the filament, as well as the distances between the tabs themselves. In this regard, installation of the separate tabs results in a labor intensive, time-consuming procedure.
Therefore, a need exists to provide a cathode assembly having a structure that simplifies integration of cathode tabs within the cathode cup thereby decreasing installation time and costs associated therewith.
The present invention provides a cathode assembly for an X-ray imaging machine. The cathode assembly includes a one-piece tab assembly for simple and relatively quick installation on a cathode cup. In one embodiment, the one-piece tab assembly has at least two rail portions extending substantially across its length. These rail portions are intended for insertion into channels formed within the cathode cup and for properly locating the one-piece tab assembly in a desired axial position on the cathode cup. The cathode assembly further includes a first tab portion and a second tab portion located on opposite ends of the rail portions. The first tab portion and the second tab portion each include a main body portion and a flap portion. The main body portion extends between the two rails and includes a mounting surface for attaching the one-piece tab assembly to the cathode cup. The flap portions extend substantially perpendicular from the main body portions and direct the electron beam emitted by the filament.
One advantage of the present invention is that a one-piece tab assembly is provided with at least two rail portions integrated therein for insertion into channels of a cathode cup and properly locating the one-piece tab assembly on the cathode cup.
Another advantage of the present invention is that a one-piece tab assembly is provided that may be properly located on the cathode cup by merely adjusting the position of the one-piece tab assembly along one axis of movement.
Still another advantage of the present invention is that a one-piece tab assembly is provided with a first tab portion and a second tab portion located at a fixed distance from each other so as to eliminate the need for adjusting the tabs relative to each other.
Yet another advantage of the present invention is that a one-piece tab assembly is provided with a main body portion for mounting the one-piece tab assembly to a cathode cup.
Other advantages of the present invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.